When grinding a stone material, the surface of the stone material as a grinding workpiece is not perfectly flat, and in a narrow sense includes slopes, undulations, and curvatures. A grinding machine is structured to enable a grinder to which grinding stone chips are attached to tilt with respect to the grinding workpiece, so that even if the stone material surface includes slopes, etc., it can be excellently ground. However, the circumferential velocity differs between the outer peripheral side and the inner peripheral side of the rotary disk, so that the movement amount per 360-degree rotation of the disk is larger on the outer peripheral side. Therefore, the degree of abrasion of the grinding stone chip on the outer peripheral side is higher than that of the grinding stone chip on the inner peripheral side, so that the grinding stone chip on the outer peripheral side cannot come into contact with the workpiece.
On the other hand, for example, in Patent Document 1 described below, by increasing the number of grinding stone chips on the outer peripheral side of the rotary disk to be larger than the number of grinding stone chips on the inner peripheral side of the rotary disk, the degrees of abrasion are substantially made uniform. In Patent Document 2 described below, by forming the grinding surfaces of the grinding chips so that their widths in the circumferential direction become narrower toward the rotary shaft core side, the abrasion amounts are made uniform.